The present disclosure and embodiments thereof are in the field of X-ray diffraction, an analytical technique that is widely used for identifying and quantifying crystalline phases present in materials. More particularly, the present disclosure relates to an apparatus and method for inducing high-speed and variable-tilt wobble motions necessary for randomizing the orientations of the crystallites present in a sample of interest, either in bulk or powder form, thereby enabling phase identification and quantification.
It is important to identify and quantify crystalline phases to understand structure-property relationships which impact final application of the material, for example ensuring reliability during production or for engineering new materials. It is also necessary to determine unknown phases formed in a material, i.e. corrosion products. The materials and their products can be used in a variety of industries and applications, which include aerospace, automotive, biomedical, ceramics, electronics, energy, metal processing, optics, and semiconductor and packaging.
Most X-ray diffraction analysis is carried out using the reflection geometry, where an X-ray source and X-ray detector are placed on either side of the sample and moved in an angular fashion, during measurement, in the same plane as the sample. The X-rays from the source are scattered or diffracted off the sample onto the X-ray detector.
An ideal sample of interest for X-ray diffraction, based on the reflection geometry, consists of randomly oriented crystallites in a powder form, where the size of the crystallites ranges from 1 to 5 microns. In reality, many samples of interest for X-ray diffraction analysis, including those in powder form, are not ideal, either because the crystallites of the samples are larger than the incoming X-ray beam used during analysis or because the crystallites in the sample are oriented along certain directions, in other words, showing crystallographic texture. As a result, incomplete or missing Debye rings are generated during the analysis process, thereby causing erroneous results during phase identification and quantification. Certain samples can be processed in a destructive manner, i.e., ground or broken down into a fine free flowing powder, for reducing the effects of crystallographic texture.
A known industry method for reducing the effects of crystallographic texture during X-ray diffraction analysis is the capillary spinner method. According to this method, a sample is broken down into a free-flowing fine powder and inserted into an X-ray transparent capillary tube. The tube is sealed at both ends, and then spun at a high speed thereby randomizing the various crystallite orientations during analysis. There are obvious inherent deficiencies associated with this method. Firstly, the sample needs to be broken into a fine powder form, which destroys the integrity of the sample and is thus destructive. Therefore, this method is not applicable to bulk samples or powders that cannot be altered in any shape or form. Secondly, the crystalline phases present in the sample can be altered or changed during sample processing, thereby preventing identification of the phases originally present in the sample.
In the case of samples that cannot be destroyed for measurement or converted into a powder form, a non-destructive method, called the wobble method, is used to reduce the effects of crystallographic texture during X-ray diffraction analysis. This is achieved by simultaneously rotating and tilting the sample during analysis, while maintaining a constant sample height at the instrument center or test center of the X-ray diffractometer. This wobble motion method does not change the shape or form of the sample and thus, is truly non-destructive. The method can effectively randomize the various crystallite orientations present in the sample relative to the X-ray source and detector, similar to the capillary spinner method, but without any sample modification or alteration. The wobble motions can be created and controlled according to special sequences as necessary.
Wobble motions can be created by using a cradle stage equipped on standard X-ray diffractonieters. However, there are certain disadvantages when using the cradle stage for this wobble motion. For example, the cradle stage is not designed for continuous tilt and rotation motions during measurement, although it is possible to create such motions. The wobble motions created using a cradle stage are slow, which extends analysis time and limits sample throughput. In addition, when a sample is tilted upwards, high torque is applied on gear assemblies of the cradle stage. Cradle stages typically utilize stepper motors for enabling precise positioning of the sample during analysis, which render the cradle stage unsuitable for creating continuous motions during sample analysis. In addition, continuous motions lead to excessive heat generation and significant wear and tear of the stepper motors and the gear assemblies, thereby damaging the cradle stage.
Accordingly, there exists a need to overcome the deficiencies and limitations described hereinabove with respect to the conventional destructive method and apparatus for reducing the effects of crystallographic texture, and the limitations of creating wobble motions on a standard cradle stage.